A NOVEL TYPE OF DNA-BINDING PROTEIN INTERACTS WITH A CONSERVED SEQUENCE IN AN EARLY NODULIN ENOD12 PROMOTER

The pea genes PsENOD12A and PsENOD12B are expressed in the root hairs shortly after infection with the: nitrogen-fixing bacterium Rhizobium leguminosarum by. viciae or after application of purified Nod factors. A 199 bp promoter fragment of the PsENOD12B gene contains sufficient information for Nod factor-induced tissue-specific expression. We have isolated a Vicia sativa cDNA encoding a 1641 amino acid protein, ENBP 1, that interacts with the 199 bp ENOD12 promoter. Two different DNA-b inding domains were identified in ENBP1. A domain containing six AT-ho oks interacts specifically with an AT-rich sequence located between po sitions -95 and -77 in the PsENOD12B promoter. A second domain in ENBP 1 is a cysteine-rich region that binds to the ENOD12 promoter in a seq uence non-specific but metal-dependent way. ENBP1 is expressed in the same cell types as ENOD12. However, additional expression is observed in the nodule parenchyma and meristem. The presence of three small ove rlapping ORFs in the 5'-untranslated region of the ENBP1 cDNA indicate s that ENBP1 expression might be regulated at the translational level. The interaction of ENBP1 with a conserved AT-rich element within the ENOD12 promoter and the presence of the ENBP1 transcript in cells expr essing ENOD12 strongly suggest that ENBP1 is a transcription factor in volved in the regulation of ENOD12. Finally, the C-terminal region of ENBP1 shows strong homology to a protein from rat that is specifically expressed in testis tissue.